Dynamic force characteristics and design of fastening system
- What are the main sources of dynamic forces borne by the fastening system?
Dynamic forces mainly come from the impact of train wheel sets, including vertical impact forces (caused by track irregularities), lateral forces (centrifugal force in curve sections and wheel-rail guiding force), and longitudinal forces (generated during train braking and acceleration). When high-speed trains pass, vertical impact forces can reach 2-3 times the static load, and lateral forces can exceed 100kN in small-radius curve sections. These dynamic forces change dynamically with train speed, axle load, and track conditions.
- What impact do dynamic forces have on elastic clips and bolts?
Dynamic forces subject elastic clips to alternating stress, prone to fatigue damage, and may cause cracks or even fractures under long-term action. Bolts will experience preload attenuation under dynamic forces, especially when lateral forces act repeatedly, with bolt loosening rate 30%-50% higher than static conditions. Dynamic forces also exacerbate friction and wear between elastic clips and rails, shortening component service life.
- How to consider dynamic forces in designing fastening systems?
During design, dynamic force peaks must be calculated through dynamic simulation. The fatigue strength of elastic clips must withstand 2 million cycles of load without cracks. Bolts are selected with high strength grades (10.9 and above) and anti-loosening structures (such as Spiralock threads), ensuring preload attenuation rate ≤5%/year. The overall stiffness of the fastening system must match the track dynamic characteristics to avoid resonance amplifying dynamic forces.
- What are the differences in dynamic design of fastening systems for different speed grade lines?
The fastening system for 350km/h high-speed railways must focus on controlling vertical dynamic forces, using high-elasticity clips (clamping force fluctuation ≤10%) and under-rail pads with good buffering performance. For 160km/h ordinary railways, lateral force control is emphasized, with elastic clip clamping force 10%-15% higher than that of high-speed railways. Heavy-haul railways (axle load ≥25t) need to strengthen longitudinal force resistance, with bolt preload 20% higher than the standard value.
- How to monitor the dynamic force status of the fastening system?
Real-time monitoring of dynamic stress changes is done through strain sensors installed on elastic clips and bolts. Regularly measure the vibration acceleration when trains pass using a track dynamic detector to indirectly evaluate the magnitude of dynamic forces. For areas with concentrated dynamic forces such as turnouts and curve sections, special inspections are conducted quarterly to promptly detect component damage and loosening.